Anyone care to hazard a guess at this printing anomaly?

Question

What's been standard and repeated for a few years:
-- The way I export TIFs and JPGs to a certain client. TIFs are tagged Adobe 1998, JPGs tagged sRGB.
-- The client's computer, a Mac G5. Client, a rep at a busy architect firm, has been printing images from me and from other photographers, without tweak or fuss, on a Canon imagePROGRAF 5100. Standard routine: launch files in old Photoshop CS, Command-P, select paper type, go.
Very nice prints, over and over, for years.
What's changed:
I recently delivered two jobs. All the files print too dark. Uniformly too dark. Monitor display is fine. Older files print fine.
The only change to either of our routines: these are the first jobs I've delivered that were generated from Lightroom 3. (Been with LR since beta.)
Not saying that's the problem. I'm just at a loss. Today I regenerated the entire job and brought it to the client. We spent an hour looking at settings, running test prints. Consistently too dark. Tried a couple variations on printer profiles. Disastrous.
This remains: these particular files print too dark. (Think at least a full stop.) Other older files print fine, as they always have. Monitor display and histograms reflect no such variation.
I'm dying to know the obvious thing I'm overlooking.
--david

Answer 1

When you say the "older files print fine," are you printing those older files directly from LR 3?
Or, are you printing those older files from Photoshop CS?